A photolithograph process is a key process in manufacturing of a display in which a pattern on a mask is transferred onto a substrate through spin-coating, exposure, and development, where a depth of focus in exposure is an important factor in the exposure process, and if a photosensitive material does not lie in the range of the depth of focus, which is referred to as exposure defocusing, while the display is being produced, then the pattern may be distorted. However in the prior art, the pattern may also be distorted due to other processes, so it may be difficult to determine whether the pattern is distorted due to exposure defocusing, and thus impossible to detect the problem of exposure defocusing in a timely manner.